Oops, I almost forgot to pick a special tower!
I searched the wiki and have no idea why the Gryphon Rider is considered a tower. It's an environmental addition, just like the magic blossoms and poisonous fruits, right?
My favorite would be the Ashbite Tower. While UP in Frontiers, I though Ashbite was still a somewhat cool hero. Here, he really has some usefulness against the spider mobs, and moving him around across nearly all of the map helped me create some awesome chokepoints with reinforcements!
I also really like the Shrine of Regnos, but that's only because it's the saving grace in Rising Tides. It loses lots of points because I don't think it's possible to complete Sunken Citadel without it, unless you're using Gnome Shop stuff.